The invention relates to an apparatus at a spinning preparatory plant for detecting foreign objects, for example, pieces of cloth, tapes, string, pieces of sheeting and the like in the fibre material, for example, cotton and/or synthetic fibres.
It is known, in a spinning preparatory installation, in which the fibre material is transportable in a current of air through a fibre transport duct or a feed chute and an optical sensor system is associated with the fibre transport duct or the feed chute, for the wall surfaces of the duct or chute to have at least one transparent region through which the sensor system detects the fibre-air flow.
In the case of a known apparatus (DE 10 2005 014 898 A1), the fibres are transported through a partially transparent channel. In this apparatus, the transparent regions of the channel are arranged flush with the non-transparent regions of the channel wall. The transparent region and the flow of fibre and air run parallel to one another. This arrangement is chosen because it is assumed that it has no affect on the flow properties and there is a belief that the transparent regions have to be protected from, that is, kept away from, the contaminating and degrading action of the fibre material. In terms of construction, this arrangement can be manufactured inexpensively. One problem in the operation of this optically functioning foreign part detector is that the necessary interface, usually glass or plastics, between the area of the fibre material flow and the area with the optical components becomes contaminated with the substances contained in the fibre material, such as dust, honeydew or finishing agents, or impurities carried along in the fibre-air flow. This contamination impairs the function of the foreign part detector, thus necessitating service intervals for cleaning that are unacceptable to the operators. The same problems exist in the application of optical measuring apparatus that looks into fibre-carrying channels of spinning preparatory machines.